Samenvatting

Thermal comfort is determined by the combined effect of the six thermal comfort parameters: temperature, air
moisture content, thermal radiation, air relative velocity, personal activity and clothing level as formulated by
Fanger through his double heat balance equations. In conventional air conditioning systems, air temperature is
the parameter that is normally controlled whilst others are assumed to have values within the specified ranges
at the design stage. In Fanger’s double heat balance equation, thermal radiation factor appears as the mean
radiant temperature (MRT), however, its impact on thermal comfort is often ignored. This paper discusses the
impacts of the thermal radiation field which takes the forms of mean radiant temperature and radiation
asymmetry on thermal comfort, building energy consumption and air-conditioning control. Several conditions
and applications in which the effects of mean radiant temperature and radiation asymmetry cannot be ignored
are discussed. Several misinterpretations that arise from the formula relating mean radiant temperature and
the operative temperature are highlighted, coupled with a discussion on the lack of reliable and affordable
devices that measure this parameter. The usefulness of the concept of the operative temperature as a measure
of combined effect of mean radiant and air temperatures on occupant’s thermal comfort is critically
questioned, especially in relation to the control strategy based on this derived parameter. Examples of systems
which deliver comfort using thermal radiation are presented. Finally, the paper presents various options that
need to be considered in the efforts to mitigate the impacts of the thermal radiant field on the occupants’
thermal comfort and building energy consumption.